The present invention pertains to mobile telecommunications and more particularly to end-to-end vocoder selection.
Mobile stations in a radio access network (RAN) and internet protocol phones in a voice over internet protocol telephony network, require vocoders in order to communicate with other IP phones or mobile stations. These IP phones or mobile stations may have different vocoder requirements.
In most telephony and wireless systems the mismatching vocoder problem is solved in a sub-optimal way by transcoding each end user to a well known vocoder for transmission through the network. Usually G.711 protocol is used for such transmission. The vocoding is set up by the end points negotiating what vocoding capability they support. Such is called transcoding between the mismatching vocoders. This transcoding may even be performed in situations where it would not be required (i.e., if the vocoders matched).
For voice over internet protocol networks which employ session initiation protocol (SIP) one of the IP phones will detect that there is a mismatch between the vocoder capabilities at the two end points. As a result the call may fail because one of the end points does not support a common vocoder arrangement to permit communication. Otherwise, the IP phone or end point may generate a request for a transcoder to be added to the call. This requires several steps through the network. Further adding the transcoder requires that the particular end point or phone know how to access and control the transcoder to be inserted into the call. Such an arrangement requires many steps and network processes. Further a substantial time delay is inserted to the call to provide transcoding services.
Accordingly, it would be highly desirable to have a vocoder selection method which is independent of the end points and provides for transparent communication between the end points without the need of vocoder selection by the end points.